Development of micro-spacecraft such as micro- and nano-satellites has expanded significantly in the last ten years with the increased miniaturization of components. The satellite user community is moving towards constellations of reprogrammable/reconfigurable autonomous systems that require numerous micro- or nano-satellites. Such satellites require a propulsion system that is sufficiently small but provides sufficient power to position the satellites in such constellations.
The design of such micro-spacecraft therefore affects the requirements of the propulsion system due to limitations related to power, mass, and fuel system complexity. The advanced propulsion systems are necessary for station keeping and orbit transfer to extend the life of the satellite, thus minimizing program launch costs and maximizing satellite lifetime value. New types of micro- and nano-thrusters are therefore needed that offer a wide range of impulse bits from nN-s to μN-s, with overall thrust efficiencies of 10-20% and very low (<1 kg) total thruster and power processing unit (PPU) mass.
A vacuum arc thruster (VAT) plasma source propulsion unit is one alternative propulsion system for micro-satellites. Such a plasma drive incorporates a cathode and anode separated by an insulator. The plasma drive includes a voltage source connected to an inductor and provides current to the inductor when a switch is enabled. The current in the inductor increases until the switch opens, which causes an arc initiation potential and an arc develops between the cathode and the anode. The plasma drive produces plasma about the external cathode-insulator interface, which is directed distally by the magnetic field. The cathode serves as the solid fuel source and propellant for the vacuum arc thruster. The thrust created by the vacuum arc thruster is dominated by pressure gradients formed by expanding plasma generated by a low voltage energy source. The efficiency and life of a vacuum arc thruster may be enhanced by a magnetic field used to direct the thrust produced. Such a vacuum arc thruster is disclosed in U.S. Patent Publication No. 2011/0258981 hereby incorporated by reference. However, even known vacuum arc thrusters are limited by the fuel contained in the cathode. Further, the vacuum arc thruster is limited in the amount of thrust generated.
Thus, there is a need for a propulsion system that has efficient use of fuel. There is a further need for a propulsion system that can vary the thrust produced based on the material of a cathode. There is a further need for a propulsion unit having electrodes that replenish as they are depleted. There is also a need to keep the propulsion system design as compact as possible for micro- or nano-satellites.